Local purge within metrology and inspection systems

ABSTRACT

A purge system includes a purge gas distribution manifold that includes at least one port through which light beam from an optical metrology or inspection head is transmitted. The purge gas distribution manifold includes a bottom surface having one or more apertures through which purge gas is expelled. The bottom surface is held in close proximity to the top surface of the substrate and the apertures may be distributed over the bottom surface of the purge gas distribution manifold so that purge gas is uniformly distributed over the entirety of the top surface of the substrate at all measurement positions of the substrate with respect to the optical metrology or inspection head.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.15/994,958, entitled “LOCAL PURGE WITHIN METROLOGY AND INSPECTIONSYSTEMS,” filed May 31, 2018, which claims benefit to and priority under35 USC § 119 to U.S. Provisional Application No. 62/595,023, entitled“LOCAL PURGE WITHIN METROLOGY AND INSPECTION SYSTEMS,” filed Dec. 5,2017, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention is related to optical metrology and inspectionsystems, and in particular to a localized purging of optical metrologyand inspection systems.

BACKGROUND

To improve process control for some semiconductor manufacturingprocesses, optical metrology and substrate inspection systems are usedto measure and quickly provide feedback for real-time control of theprocesses. Metrology and substrate inspection processes in semiconductormanufacturing, however, are vulnerable to Airborne MolecularContamination (AMC) as well as moisture within the environment.Additionally, the substrates themselves are also vulnerable to AMC andmoisture in the environment, which may produce contaminants on thesurface of a substrate or form film growth or corrosion/oxidation.Moreover, the use of AMC filtration may reduce film growth rate, butdoes not address humidity control effectively enough to preventcorrosion/oxidation.

Purge systems are sometimes used to protect the metrology and substrateinspection systems and/or substrates under test. By way of example,purge systems sometimes use a purged chamber into which a purge gas orclean dry air is provided. Use of purged chamber, however, requires nearvacuum chamber sealing integrity to the atmosphere, and significantsafety controls to protect service personnel from asphyxiation hazards.Moreover, a significant amount of purge gas or air may be required toadequately purge a chamber. Other purge systems provide a purge gas orair to the beam path of the optical metrology or inspection device.Thus, purge gas or air contacts limited areas of the substrate duringtesting, but the remainder of the substrate may still be exposed to theatmosphere including AMC and humidity. Accordingly, improvements overconventional purge systems are desired.

SUMMARY

A purge system includes a purge gas distribution manifold that includesat least one port through which a light beam from an optical metrologyor inspection head is transmitted. The purge gas distribution manifoldincludes a bottom surface having one or more apertures through whichpurge gas is expelled. The bottom surface is held in close proximity tothe top surface of the substrate and the apertures are distributed overthe bottom surface of the purge gas distribution manifold so that purgegas is uniformly distributed over the entirety of the top surface of thesubstrate at all measurement positions of the substrate with respect tothe optical metrology or inspection head.

In one implementation, an apparatus includes an optical metrology orinspection head that produces a light beam that is incident on asubstrate to be optically measured and is received by the opticalmetrology or inspection head after interacting with the substrate, achuck for holding the substrate, wherein at least one of the chuck andthe optical metrology or inspection head is movable to position thesubstrate at a plurality of measurement positions with respect to theoptical metrology or inspection head, a purge gas distribution manifoldcoupled to a purge gas source, the purge gas distribution manifoldhaving at least one port through which the light beam is transmitted,the purge gas distribution manifold having a bottom surface that is 25mm or less from a top surface of the substrate and has a plurality ofapertures through which purge gas is expelled over the top surface ofthe substrate, wherein the plurality of apertures are distributed over asurface area that is at least as large as a surface area of the topsurface of the substrate to distribute the purge gas over an entirety ofthe top surface of the substrate at all measurement positions of thesubstrate with respect to the optical metrology or inspection head.

In one implementation, an apparatus includes an optical metrology orinspection head that produces a light beam that is incident on asubstrate to be optically measured and is received by the opticalmetrology or inspection head after interacting with the substrate, achuck for holding the substrate, wherein at least one of the chuck andthe optical metrology or inspection head is movable to position thesubstrate at a plurality of measurement positions with respect to theoptical metrology or inspection head, a purge gas distribution manifoldcoupled to a purge gas source, the purge gas distribution manifoldhaving at least one port through which the light beam is transmitted,wherein there is relative motion between the purge gas distributionmanifold and the substrate when the at least one of the chuck and theoptical metrology or inspection head is moved to position the substrateat the plurality of measurement positions with respect to the opticalmetrology or inspection head, the purge gas distribution manifold havinga plurality of apertures through which purge gas is expelled over a topsurface of the substrate, wherein the plurality of apertures aredistributed over a surface area that is larger than a surface area ofthe top surface of the substrate to distribute the purge gas over anentirety of the top surface of the substrate at all measurementpositions of the substrate with respect to the optical metrology orinspection head.

In one implementation, an apparatus includes an optical metrology orinspection head that produces a light beam that is incident on asubstrate to be optically measured and is received by the opticalmetrology or inspection head after interacting with the substrate, achuck for holding the substrate, wherein at least one of the chuck andthe optical metrology or inspection head is movable to position thesubstrate at a plurality of measurement positions with respect to theoptical metrology or inspection head, a purge gas distribution manifoldcoupled to a purge gas source, the purge gas distribution manifoldhaving at least one port through which the light beam is transmitted,the purge gas distribution manifold is held linearly stationary withrespect to the substrate when the at least one of the chuck and theoptical metrology or inspection head is moved to position the substrateat the plurality of measurement positions with respect to the opticalmetrology or inspection head, the purge gas distribution manifold havinga plurality of apertures through which purge gas is expelled, wherein adistribution area of the plurality of apertures is within 25 percent ofa surface area of a top surface of the substrate to distribute the purgegas over an entirety of the top surface of the substrate at allmeasurement positions of the substrate with respect to the opticalmetrology or inspection head.

In one implementation, an apparatus includes an optical metrology orinspection head that produces a light beam that is incident on asubstrate to be optically measured and is received by the opticalmetrology or inspection head after interacting with the substrate, achuck for holding the substrate, wherein at least one of the chuck andthe optical metrology or inspection head is movable to position thesubstrate at a plurality of measurement positions with respect to theoptical metrology or inspection head, a ceiling having at least one portthrough which the light beam is transmitted, the ceiling having a bottomsurface that is 25 mm or less from a top surface of the substrate; and afence surrounding the substrate on the chuck, wherein the fence is heldlinearly stationary with respect to the substrate when the at least oneof the chuck and the optical metrology or inspection head is moved toposition the substrate at the plurality of measurement positions withrespect to the optical metrology or inspection head, the fence havingone or more apertures below the top surface of the substrate and throughwhich purge gas is expelled over the top surface of the substrate todistribute the purge gas over an entirety of the top surface of thesubstrate at all measurement positions of the substrate with respect tothe optical metrology or inspection head.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a side view of a purge system with a purge gasdistribution manifold that provides a localized clean environment forthe top side of a substrate.

FIGS. 2A and 2B illustrate embodiments of a bottom surface of the purgegas distribution manifold.

FIGS. 3 and 4 illustrate cross-sectional views of a portion of the purgegas distribution manifold showing different embodiments of ports.

FIG. 5 illustrates a side view of a purge system with a purge gasdistribution manifold that includes a plurality of zones and provides alocalized clean environment for the top side of a substrate with areduced purge gas flow.

FIG. 6 is a plan view of a plurality of zones of the purge gasdistribution manifold and the substrate located at a measurementposition.

FIG. 7 illustrates a side view of a purge system that moves with thesubstrate to different measurement positions.

FIG. 8 illustrates a side view of portions of the purge gas distributionmanifold and the substrate.

FIG. 9 illustrates a plan view of a purge gas distribution manifold thatis approximately the same size as the substrate.

FIGS. 10A and 10B illustrate side views of a portion of a purge gasdistribution manifold and a portion of a fence that surrounds asubstrate.

FIG. 11 illustrates a plan view of a purge gas distribution manifold anda fence that surrounds a substrate and reference chip.

FIG. 12 illustrates a side view of a purge system in which purge gas isprovided into the localized environment around the substrate through afence.

DETAILED DESCRIPTION

FIG. 1 illustrates a side view of a purge system 100 that provides apurged environment to the entirety of the top side of a substrate 102being inspected or measured. The purged environment is localized to thesurface of the substrate 102, as opposed to the entire environmentsurrounding the substrate 102 or metrology or inspection device, e.g.,as in a conventional purge chamber. The purge system 100 includes apurge gas distribution manifold 110 that distributes the purge gas andis positioned so that only a small gap is between a bottom surface 118of the purge gas distribution manifold 110 and the top surface 104 ofthe substrate 102. For example, the bottom surface 118 of the purge gasdistribution manifold 110 may be 25 mm or less from the top surface 104of the substrate 102. The small gap between the purge gas distributionmanifold 110 and the substrate 102 minimizes the purge gas consumptionwhile providing good shielding purity in the local environment over thesubstrate 102.

The purge gas distribution manifold 110 is fluidically coupled to apurge gas source 112, which may supply an inert gas, such as nitrogen orargon or air, which is purified clean dry air, a combination thereof, orany other suitable inert gas. The purge gas distribution manifold 110includes a distribution plenum 114, which distributes the purge gas fromthe inlet 116 coupled to the purge gas source 112 and distributes thepurge gas over a large area within the purge gas distribution manifold110. The bottom surface 118 of the purge gas distribution manifold 110includes a plurality of apertures 120 through which the purge gas fromthe distribution plenum 114 is expelled, as illustrated by the arrows.

FIGS. 2A and 2B illustrate different implementations of the bottomsurface 118 of the purge gas distribution manifold 110 relative to asubstrate 102. FIG. 2A illustrates an implementation of the purge gasdistribution manifold 110, where the substrate is positioned formeasurement using Cartesian coordinate plane (X,Y) directions and FIG.2B illustrates an implementation where the substrate is moved in thePolar coordinate plane (R, θ). As illustrated, apertures 120 in thebottom surface may be holes uniformly or non-uniformly distributed overthe area of the bottom surface 118. If desired, as illustrated in FIG.2B, distribution grooves 122 may be coupled to the holes in the bottomsurface 118 in order to assist in a uniform distribution of the purgegas. By way of example, the holes may be 10 mm or less, e.g., 2 mm, indiameter, and there may be between 1 mm to 25 mm between the holes ifthere are no distribution grooves. With the use of distribution grooves,which may be, e.g., 2 mm-10 mm wide, fewer holes may be required and thespacing between holes may be increased, e.g., up to 50 mm-75 mm betweenholes. Moreover, with distribution grooves, a greater flow rate may bedesired, and thus holes with a larger diameter, e.g., 10 mm, may beused. Additionally, the size of the holes may selected as a function ofposition in the bottom surface 118 of purge gas distribution manifold110 to balance the flow rates for uniform protection over the entiresurface of the substrate 102. It should be understood, however, thatwhile the general shape of the purge gas distribution manifold 110 mayvary based on how the substrate moves, the specific implementation ofthe bottom surface of the purge gas distribution manifold 110 is notlimited to movement of the substrate in any particular coordinatesystem.

In another implementation, the bottom surface 118 of the purge gasdistribution manifold 110 or portions of the bottom surface 118 may be aporous media, such as a porous carbon or polymer, or sintered metal orpolymer, where the purge gas is expelled through the apertures, i.e.,pores, in the porous media. In some implementations, a porous media maybe located within apertures, which may be 25 mm or less in diameter, inthe bottom surface 118 to the throttle the flow of the purge gas and toprovide a uniform distribution of gas over the substrate surface. Theporous media, apertures and distribution grooves may be used together,or alternatively, the porous media and apertures, without distributiongrooves, may be uniformly or non-uniformly distributed over the area ofthe bottom surface 118.

By positioning the purge gas distribution manifold 110 close to the topsurface 104 of the substrate 102 and the use of the plurality ofapertures 120 distributed over the bottom surface 118 of the purge gasdistribution manifold 110, a uniform distribution of the purge gas overthe entirety of the top surface 104 of the substrate 102 may be producedwith only a modest flow rate of purge gas. By way of example, modelinghas shown flow rates on the order of 1 cfm may reduce O2 levels below0.02%, and further design optimization may yield even further reducedflow rates at similar O2 concentrations. For some applications, the flowrate may be controlled and reduced via a software recipe control, or bysetting a lower flow rate passively. An exhaust port (not shown) may beprovided, e.g., below the stage 108, to remove the purge gas.

As illustrated in FIG. 1, the purge system 100 is used with an opticalmetrology or inspection head 130 that may include one or more metrologyor inspection devices. Optical metrology or inspection head 130 isillustrated as including objective lenses 131 a, 131 b, which producelight beam 132 that is obliquely incident on the substrate 102, and anobjective lens 131 c, which produces light beam 134 that is normallyincident on the substrate 102. The objective lenses 131 a, 131 b, by wayof example, may be part of an ellipsometer or other instrument that usesobliquely incident light. The light beam 132 may be emitted by objectivelens 131 a and received by objective lens 131 b after interacting withthe substrate 102. The object lens 131 c, by way of example, may be areflectometer or other instrument that uses normally incident light. Thelight beam 134 is emitted by objective lens 131 c and received byobjective lens 131 c after interacting with the substrate 102. For thesake of simplicity, the optical metrology or inspection head 130 isillustrated as only objective lenses, but it should be understood thatadditional optical elements, such as a light source, detector,polarizing elements, etc., are included in an optical metrology orinspection device, but illustrations of these additional elements areunnecessary for understanding the operation of the purge system 100.

The purge gas distribution manifold 110 includes one or more ports 124through which the light beams 132 and 134 from an optical metrology orinspection head 130 is transmitted to and from the substrate 102. Thepurge gas distribution manifold 110 may include two separate ports 124that are slanted with respect to the bottom surface 118 to accommodatethe obliquely incident light from the optical metrology or inspectionhead 130 and a port 124 that is perpendicular to the bottom surface 118to accommodate the normally incident beam 134. If desired, a singlelarge port 124 may be used with the obliquely incident light beam 132and normally incident light beam 134 of the optical metrology orinspection head 130, but this may affect distribution of the purge gasover the substrate 102.

The port(s) 124 in the purge gas distribution manifold 110 may be, e.g.,apertures passing through the purge gas distribution manifold 110. Forexample, as illustrated in a closer view of the ports 124 in FIG. 3, theports 124 may pass through and may be fluidically coupled to thedistribution plenum 114 and, thus, purge gas may be expelled through theport(s) 124 as illustrated by arrows 126. In another implementation, asillustrated in a closer view of the ports 124 in FIG. 4, the ports 124may not be fluidically coupled to the distribution plenum 114.

The substrate 102 is held by a chuck 106 that may be coupled to a stage108. Additionally, or alternatively, the optical metrology or inspectionhead 130 may be coupled to a stage (not shown). The stage 108 (and/orthe stage coupled to the optical metrology or inspection head 130,produces relative motion between the chuck 106 (with substrate 102) andthe optical metrology or inspection head 130 so that at least one of thechuck 106 and the optical metrology or inspection head 130 is movable toposition the substrate 102 at a plurality of measurement positions withrespect to the optical metrology or inspection head 130. For example,the stage 108 may move the substrate 102 linearly, e.g., within theCartesian coordinate plane (X,Y) directions, or may rotate and linearlymove the substrate 102, e.g., in Polar coordinate plane (R, θ). Ifdesired, the substrate 102 and the optical metrology or inspection head130 may both be moved, e.g., the substrate 102 may rotate while theoptical metrology or inspection head 130 moves linearly. Alternatively,the optical metrology or inspection head 130 may move while thesubstrate 102 is held stationary. In implementations where the opticalmetrology or inspection head 130 moves linearly, it should be understoodthat the purge gas distribution manifold 110 may move with the opticalmetrology or inspection head 130.

As illustrated in FIG. 1, the bottom surface 118 of the purge gasdistribution manifold 110 may be significantly larger than the substrate102. The plurality of apertures 120 are distributed over a surface areathat is larger than the surface area of a top surface of the substratein order to distribute the purge gas over an entirety of the top surfaceof the substrate at all measurement positions of the substrate withrespect to the optical metrology or inspection head. In oneimplementation, e.g., where Cartesian coordinate are used as illustratedby FIG. 2A, diameter of the purge gas distribution manifold 110 may betwice that of the substrate 102 or more, e.g., the plurality ofapertures 120 may be distributed over a surface area that is at leastfour times the surface area of the substrate 102. In an implementationin which Polar coordinates are used as illustrated by FIG. 2B, the sizeof the purge gas distribution manifold 110 may be reduced so that theplurality of apertures 120 may be distributed over a surface area thatis approximately 2.3 times the surface area of the substrate 102.Accordingly, as the relative motion between the substrate 102 and theoptical metrology or inspection head 130 to place the substrate 102 indifferent measurement positions with respect to the optical metrology orinspection head 130, the entirety of the substrate 102 remains under thedistribution of apertures 120 in the purge gas distribution manifold 110at all measurement positions of the substrate 102. Thus, the purge gasdistribution manifold 110 uniformly distributes the purge gas over theentire top surface 104 of the substrate 102 at all measurement positionsresulting in an effective coverage protecting the top surface 104 of thesubstrate 102 from environmental chemical, humidity, or particlecontaminants, with minimal flow of the purge gas.

Additionally, as illustrated in FIG. 1, a reference chip 140 may becoupled to the stage 108. The reference chip 140 may be, e.g., a baresilicon chip, or other appropriate chip that may be used to calibratethe optical metrology or inspection device. As optical metrology orinspection device may be sensitive to any changes in the opticalproperties of the reference chip 140, the purge gas distributionmanifold 110 may be used to additionally provide purge gas to thereference chip 140. If desired, however, a separate purge system may beused with the reference chip 140.

The substrate 102 may be loaded onto the chuck 106, e.g., by loweringthe chuck 106 to allow an end effector to place the substrate 102 onpins in the chuck 106, and the chuck 106 may then be raised to a desiredheight to hold the substrate 102 on the chuck surface. Alternatively,the purge gas distribution manifold 110 may have a step with greaterclearance at the location where the substrate 102 is loaded onto thechuck, where the step has sufficient height to allow the end effector toplace the substrate 102 on the chuck 106. With the presence of a step ina portion of the purge gas distribution manifold 110, an increased flowrate may be used in the location of the step in order to maintain purgepurity.

In one implementation, the purge gas distribution manifold may bepartitioned into a plurality of zones, where the flow of purge gas isswitched on or off at different zones depending on whether the substrateis present or absent from each zone when the substrate is moved todifferent measurement positions. FIG. 5, by way of example, illustratesa side view of a purge system 200 that includes a plurality of zones toprovide a localized clean environment for the top side of a substrate102 when the substrate 102 is present within any zone, while theremaining zones have a reduced flow of purge gas. Purge system 200 issimilar to purge system 100 shown in FIG. 1, like designated elementsbeing the same. Purge system 200 includes a purge gas distributionmanifold 220 that is positioned, e.g., 25 mm or less, from the topsurface 104 of the substrate 102. The purge gas distribution manifold220 includes a distribution plenum 224 that includes multiple zones Z1,Z2, Z3, each of which is fluidically coupled to a purge gas source 112through valves 226 _(Z1), 226 _(Z2), 226 _(Z3) (sometimes collectivelyreferred to as valves 226) that independently control the flow of purgegas to their associated zones. Each valve 226 may be controlled toreduce or stop the flow of purge gas to an associated zone, for example,when the substrate 102 is not present under an associated zone.Additionally, associated with each valve 226 _(Z1), 226 _(Z2), 226 _(Z3)is a bypass valve 228 _(Z1), 228 _(Z2), 228 _(Z3) (sometimescollectively referred to as bypass valves 228). Each bypass valve 228provides a reduced flow of purge gas to the associated zones in thedistribution plenum 224 to maintain a charge of purge gas within theassociated zone of the distribution plenum 224 when the valve to theassociated zone is turned off. If a reference chip 140 is included, thevalves 226 and bypass valves 228 may be controlled to provide purge gasto any zone in which the reference chip is present.

The valves 226 and bypass valves 228 may be controlled by controller240, e.g., based on the known position of the stage 108. The controller240 may be, e.g., a processor that controls movement of the stage 108,and thus, the substrate 102 to its different measurement positions. Inanother implementation, the valves 226 and bypass valves 228 may becontrolled based on sensors, e.g., light sensors (not shown), thatdetect the presence of the substrate 102 within each zone. For someapplications, the flow rate may be controlled via a software recipecontrol or by setting a lower flow rate passively.

FIG. 6 is a plan view of the purge gas distribution manifold 220illustrating a plurality of zones Z1, Z2, Z3, Z4, Z5, Z6, Z7, Z8, andZ9. The substrate 102 is illustrated in FIG. 6 with dotted lines at ameasurement position. The optical metrology or inspection head 130 isnot illustrated in FIG. 6, but the location that measurements areperformed by the optical metrology or inspection head 130 is illustratedat the center of the purge gas distribution manifold 220 and isillustrated with spot 131. The substrate 102 is positioned for ameasurement at the outer diameter of the substrate 102. As can be seen,the substrate 102 is present only in zones Z2, Z3, Z6 and Z7.Accordingly, valves 226 associated with zones Z2, Z3, Z6 and Z7 arecontrolled to produce a flow of purge gas. The valves 226 at theremaining zones, i.e., zones Z1, Z4, Z5, Z8, and Z9 may be controlled toreduce or stop the flow of purge gas. The bypass valves 228 at theremaining zones, i.e., zones Z1, Z4, Z5, Z8, and Z9, may be controlledto provide a minimum flow rate to keep gas purity high in thedistribution plenum 224.

It should be understood that while FIGS. 5 and 6 illustrate three andnine zones, respectively, of the purge gas distribution manifold 220,additional or fewer zones may be used to minimize the amount of purgegas used, while maintaining an effective coverage protecting thesubstrate 102.

FIG. 7 illustrates a side view of another purge system 300 that issimilar to purge system 100 shown in FIG. 1, like designated elementsbeing the same. The purge system 300 includes a purge gas distributionmanifold 320 that is approximately the same size as the substrate 102and moves linearly with the substrate 102 so that the purge gasdistribution manifold 320 is stationary relative to the substrate 102for all linear movement of the substrate 102, i.e., the purge gasdistribution manifold 320 is linearly stationary with respect to thesubstrate 102, but there may be relative rotational movement between thesubstrate 102 and the purge gas distribution manifold 320, e.g., as in aPolar coordinate (R, θ) movement. As illustrated in FIG. 7, the purgegas distribution manifold 320 includes a distribution plenum 324 that isfluidically coupled to a purge gas source 112 by a flexible connector326. The purge gas distribution manifold 320 may be coupled to the chuck106 through the stage 108 so that the purge gas distribution manifold320 is held linearly stationary with respect to the substrate 102 whenat least one of the chuck and the optical metrology or inspection headis moved to position the substrate at the plurality of measurementpositions with respect to the optical metrology or inspection head. Ifdesired, the substrate 102 may rotate with respect to the purge gasdistribution manifold 320, e.g., when Polar coordinate motion is used.The flexible connector 326 may be routed through the connection betweenthe stage 108 and the purge gas distribution manifold 320.

It should be understood that the optical metrology or inspection head130 may move in addition to or instead of the substrate 102, but thepurge gas distribution manifold 320 will remain stationary with respectto the substrate 102 for all linear movement. For example, as discussedabove, the substrate 102 and the optical metrology or inspection head130 may both be moved, e.g., the substrate 102 may rotate while theoptical metrology or inspection head 130 moves linearly. Alternatively,the optical metrology or inspection head 130 may move while thesubstrate 102 is held stationary. The purge gas distribution manifold320 may include elongated ports (or slots) or additional ports toaccommodate movement of the optical metrology or inspection head 130 orsubstrate 102 to different measurement positions.

With the purge gas distribution manifold 320 held stationary withrespect to the substrate 102 for all linear movement, the purge gasdistribution manifold 320 does not need to be larger than the substrate102 to cover the entire top surface 104 at all measurement positions ofthe substrate 102. The purge gas distribution manifold 320 may beapproximately the same size as the substrate 102 to achieve the desiredlocalized purged environment. If desired, the purge gas distributionmanifold 320 may be slightly smaller than the substrate 102 and anadequate localized purged environment over the substrate 102 may bemaintained for all measurement positions.

FIG. 8, by way of example, illustrates a side view of portions of thepurge gas distribution manifold 320 and the substrate 102 andillustrates a possible size relationship between the purge gasdistribution manifold 320 and the substrate 102. As illustrated in FIG.8, the purge gas distribution manifold 320 is positioned a height Habove the top surface of the substrate 102, which may be, e.g., 25 mm orless. The closer the purge gas distribution manifold 320 is to thesubstrate 102, i.e., a smaller height H, the smaller the purge gasdistribution manifold 320 may be relative to the substrate 102 and lesspurge gas will be required to produce a desired localized purgeenvironment over the entire surface of the substrate 102. With use of asmall height H, however, loading the substrate 102 onto the chuck mayrequire additional actions, such as lowering and raising the chuck toaccommodate an end effector, which will increase the time that thesubstrate 102 is not within the localized purged environment and isexposed to the atmosphere.

As illustrated in FIG. 8, the substrate 102 may include an edgeexclusion zone 402, which may be a distance D₄₀₂, typically 2 mm,between the edge of the substrate 102 and the area 103 on the substratewhere dies are fabricated. Thus, it should be clear that the purge gasdistribution manifold 320 need not extend to the edge of the substrate102 in order to provide an adequate localized purged environment overthe usable area of the substrate 102. As illustrated, the end of thepurge gas distribution manifold 320 may, but is not necessarily requiredto, extend past the usable area of the substrate 102, i.e., over theedge exclusion zone 402. Thus, the end of the purge gas distributionmanifold 320 may be a distance D₃₂₀ from the edge of the substrate 102,which for a 300 mm substrate may be 0 mm or up to 5 mm, e.g.,specifically may be 2 mm (i.e., to the edge exclusion zone 402). Thus,the purge gas distribution manifold 320 may be the same size as thesubstrate 102 or may have a diameter that is up to 10 mm, or may beapproximately 10%, smaller than the substrate 102. It should beunderstood that, if desired, the purge gas distribution manifold 320 maybe larger than the substrate 102, but this may utilize more purge gas.

Additionally, as illustrated in FIG. 8, the purge gas distributionmanifold 320 includes a surface area 404 over which the plurality ofapertures are distributed, which may be smaller than the usable area ofthe substrate 102, i.e., the distribution area 404 of the apertures maynot extend over the edge exclusion zone 402. As illustrated, thedistribution area 404 of the apertures may be a distance D₄₀₄ from theedge of the substrate 102, which for a 300 mm substrate may be from 0 mmto 10 mm or from 0 mm to 20 mm. Thus, the distribution area 404 of theapertures may be the same size as the substrate 102 or may have adiameter that is up to 40 mm, or approximately 25%, smaller than thesubstrate 102. Moreover, with sufficiently small clearance between thepurge gas distribution manifold 320 and the substrate 102, i.e., heightH, it may be possible for the distribution area 404 of the apertures tobe approximately 50% smaller than the substrate 102, while stillproviding an adequate localized purged environment to the entire surfaceof the substrate in all measurement positions. For example, someapplications may benefit even from modest improvements in dryness,Airborne Molecular Contamination (AMC) cleanliness or O2 reduction. Itshould be understood that, if desired, the distribution area 404 of theapertures of the purge gas distribution manifold 320 may be larger thanthe substrate 102, but this may utilize more purge gas.

FIG. 9 illustrates a top plan view of purge gas distribution manifold320 and a substrate 102 and its edge exclusion zone 402 shown withbroken lines. As illustrated, the purge gas distribution manifold 320may include one or more linear ports 322 or slots that are the length ofa full radius of the substrate 102, which permits the light beams, suchas obliquely incident light beam 132 and normally incident light beam134, to access the substrate 102. The purge gas distribution manifold320 and a substrate 102 are held linearly stationary with respect toeach other, so that as the substrate 102 is moved linearly to differentmeasurement positions, or alternatively, as the optical metrology orinspection head 130 is moved linearly with respect to the substrate 102and the purge gas distribution manifold 320, the purge gas distributionmanifold 320 remains stationary with respect to the substrate 102 and,accordingly, will continue to provide a localized purge environment tothe entire surface of the substrate 102 at all measurement positions.Moreover, because the size of the purge gas distribution manifold 320 ismuch reduced compared to the purge gas distribution manifold 110 shownin FIG. 1, less purge gas is required by the purge gas distributionmanifold 320.

Additionally, as illustrated in FIG. 9, the reference chip 140 may beused with the purge system 300 where, for example, the purge gasdistribution manifold 320 is extended to cover the reference chip 140.If desired, one or more purge apertures 120 in the purge gasdistribution manifold 320 may be located over the reference chip 140.

If desired, additional components may be included with the purge system300, which may assist in providing a localized purge environment whileminimizing the purge gas flow rate. For example, a fence may surroundthe substrate 102 to contain and direct the purge gas. FIG. 10A, by wayof example, illustrates a side view of a portion of a fence 340 thatsurrounds the substrate 102. If a reference chip is present (not shownin FIG. 10A), both the substrate 102 and the reference chip may besurrounded by the fence 340. The fence 340 may have a fixed height andmay be coupled to the stage 108 so that the fence 340 moves linearlywith the chuck 106 and substrate 102. As with the purge gas distributionmanifold 320, if desired, the chuck 106 and substrate 102 may bepermitted to rotate with respect to the fence 340. During substrate loadand unload, the fence 340 may move downward with the stage 108 to allowan end effector to place the substrate 102 on or remove the substrate102 from pins in the chuck 106, and the chuck 106 may then be raised toa desired height. If desired, the fence 340 may move independently ofthe Z stage.

The fence 340 may include an upper surface 342 that is positioned nearthe bottom surface 318 of the purge gas distribution manifold 320. Forexample, the vertical gap 341 between the upper surface 342 of the fence340 and the bottom surface 318 of the purge gas distribution manifold320 may be 10 mm or less. The fence 340 may include one or more, e.g., 1to 150, apertures 344, which may be, e.g., up to 25 mm in diameter,through which the purge gas may be exhausted passively or actively,e.g., using a pump. By way of example, the apertures 344 may be locatedbelow the top surface of the substrate 102, such as on a bottom surface346 of the fence 340.

FIG. 10B illustrates a portion of a side view of another implementationof the fence 340 that surrounds the substrate 102. As illustrated inFIG. 10B, the apertures 344 may be fluidically coupled to a purge gassource 350 (which may be the same or a different purge gas source thatis fluidically coupled to the purge gas distribution manifold 320. Purgegas may be emitted by the one or more apertures 344, which may belocated below the top surface of the substrate 102, e.g., on the bottomsurface 346 of the fence 340. Alternatively, the fence 340 may notinclude apertures 344. The purge gas that is emitted by the purge gasdistribution manifold 320 may not be exhausted through apertures in thebottom surface 346 of the fence 340, but rather through the vertical gap341 between the upper surface 342 of the fence 340 and the bottomsurface 318 of the purge gas distribution manifold 320, as illustratedby the arrows. Purge gas emitted by the apertures 344 in the fence 340,if used, may likewise be exhausted through the vertical gap 341.

FIG. 11 illustrates a top plan view of purge gas distribution manifold320 with the fence 340, where the substrate 102 and its edge exclusionzone 402 are shown with broken lines. FIG. 11 is similar FIG. 9, likedesignated elements being the same. As illustrated, fence 340 surroundsthe substrate 102, as well as the reference chip 140, if used. The purgegas distribution manifold 320 may extend beyond the outside edge of theupper surface 342 of the fence 340. The apertures 344 in the bottomsurface 346 of the fence 340 may be underneath the substrate 102. Thefence 340, along with the purge gas distribution manifold 320 may beheld linearly stationary with respect to the substrate 102, i.e., sothat they are held stationary with respect to each other during linearmovement, but there may be relative rotational movement. Thus, the fence340 and purge gas distribution manifold 320 will provide a localizedpurge environment to the entire surface of the substrate 102 at allmeasurement positions.

If desired, the purge gas may be provided through the fence to produce alocalized purge environment above the substrate 102. FIG. 12, by way ofexample, illustrates a side view of a purge system 400 in which purgegas is provided into the localized environment around the substrate 102through a fence 410. The purge system 400 shown in FIG. 12, is similarto that shown in FIGS. 10A and 10B, like designated elements being thesame. As illustrated, purge gas may be provided from a purge gas source430 through one or more apertures 414 (e.g., 1 to 150 apertures) in thefence 410 which surrounds the substrate 102 to contain and direct thepurge gas over the top surface of the substrate 102. The apertures 414may be, e.g., up to 25 mm in diameter and may be located below the topsurface of the substrate 102, e.g., on the bottom surface 416 of thefence 410. Similar to the fence shown in FIGS. 10A and 10B, the fence410 may have a fixed height and may be coupled to the stage 108 so thatthe fence 410 moves linearly with the chuck 106 and substrate 102. Thefence 410 may include an upper surface 412 that is positioned near thebottom surface 422 of a ceiling 420, e.g., 10 mm or less. Similar to thepurge gas distribution manifold 320, the bottom surface 422 of theceiling 420 may be positioned 25 mm or less from the top surface 104 ofthe substrate 102 to minimize the purge gas consumption while providinggood shielding purity in the local environment over the substrate 102.

The ceiling 420 may be coupled to the stage 108 and may be linearlystationary with respect to the chuck 106, substrate 102 and fence 410,i.e., there is no relative movement between the ceiling 420 and thechuck 106, substrate 102 and fence 410 during linear motion, butrelative rotational movement may be permitted. Alternatively, theceiling 420 may be coupled to the optical metrology or inspection head130 so that there is relative linear and rotational movement between theceiling 420 and the chuck 106, substrate 102, and fence 410. Thus,relative movement using Cartesian coordinates or Polar coordinates ispossible. The ceiling 420 may include apertures 424 (or slots) throughwhich light beams 132 and 134 from the optical metrology or inspectionhead 130 may be transmitted. As illustrated by the arrow, the purge gasmay be exhausted through apertures 424, or may be exhausted throughother apertures (not shown) above the top surface of the substrate 102.Similar to fence 340, during substrate load and unload, the fence 410may move downward with the stage 108 to allow an end effector to placethe substrate 102 on or remove the substrate 102 from pins in the chuck106, and the chuck 106 may then be raised to a desired height. Ifdesired, the fence 410 may move independently of the Z stage.

Although the present invention is illustrated in connection withspecific embodiments for instructional purposes, the present inventionis not limited thereto. Various adaptations and modifications may bemade without departing from the scope of the invention. Therefore, thespirit and scope of the appended claims should not be limited to theforegoing description.

What is claimed is:
 1. An apparatus comprising: an optical metrology orinspection head that produces a light beam that is incident on asubstrate to be optically measured and is received by the opticalmetrology or inspection head after interacting with the substrate; achuck for holding the substrate, wherein at least one of the chuck andthe optical metrology or inspection head is movable to position thesubstrate at a plurality of measurement positions with respect to theoptical metrology or inspection head; a purge gas distribution manifoldcoupled to a purge gas source, the purge gas distribution manifoldhaving at least one port through which the light beam is transmitted,wherein there is relative motion between the purge gas distributionmanifold and the substrate when the at least one of the chuck and theoptical metrology or inspection head is moved to position the substrateat the plurality of measurement positions with respect to the opticalmetrology or inspection head, the purge gas distribution manifold havinga plurality of apertures through which purge gas is expelled over a topsurface of the substrate, wherein the plurality of apertures aredistributed over a surface area that is larger than a surface area ofthe top surface of the substrate to distribute the purge gas over anentirety of the top surface of the substrate at all measurementpositions of the substrate with respect to the optical metrology orinspection head.
 2. The apparatus of claim 1, wherein the purge gascomprises an inert gas.
 3. The apparatus of claim 2, wherein the inertgas comprises at least one of clean dry air, nitrogen, argon or acombination thereof.
 4. The apparatus of claim 1, wherein the pluralityof apertures in the purge gas distribution manifold is formed by aporous media.
 5. The apparatus of claim 1, wherein the plurality ofapertures in the purge gas distribution manifold is a pattern of holes.6. The apparatus of claim 5, wherein the holes are coupled todistribution grooves.
 7. The apparatus of claim 1, wherein the purge gasdistribution manifold is partitioned into a plurality of zones, thepurge gas distribution manifold further comprises a plurality of valvescoupled to the purge gas source, wherein each zone is associated with atleast one valve, each valve being controlled to reduce or stop a flow ofpurge gas to an associated zone when the substrate is not present withinthe associated zone.
 8. The apparatus of claim 7, further comprising aplurality of bypass valves associated with each valve, wherein eachbypass valve provides a reduced flow of purge gas to maintain a chargeof purge gas within an associated zone when an associated valve is shutoff.
 9. The apparatus of claim 1, further comprising a fence surroundingthe substrate on the chuck, wherein the fence is held linearlystationary with respect to the substrate when the at least one of thechuck and the optical metrology or inspection head is moved to positionthe substrate at the plurality of measurement positions with respect tothe optical metrology or inspection head.
 10. The apparatus of claim 9,wherein the fence comprises an upper surface that is 10 mm or less froma bottom surface of the purge gas distribution manifold.
 11. Theapparatus of claim 1, further comprising a reference chip, wherein thepurge gas distribution manifold extends over the reference chip.
 12. Anapparatus comprising: an optical metrology or inspection head thatproduces a light beam that is incident on a substrate to be opticallymeasured and is received by the optical metrology or inspection headafter interacting with the substrate; a chuck for holding the substrate,wherein at least one of the chuck and the optical metrology orinspection head is movable to position the substrate at a plurality ofmeasurement positions with respect to the optical metrology orinspection head; a purge gas distribution manifold coupled to a purgegas source, the purge gas distribution manifold having at least one portthrough which the light beam is transmitted, the purge gas distributionmanifold is held linearly stationary with respect to the substrate whenthe at least one of the chuck and the optical metrology or inspectionhead is moved to position the substrate at the plurality of measurementpositions with respect to the optical metrology or inspection head, thepurge gas distribution manifold having a plurality of apertures throughwhich purge gas is expelled, wherein a distribution area of theplurality of apertures is within 25 percent of a surface area of a topsurface of the substrate to distribute the purge gas over an entirety ofthe top surface of the substrate at all measurement positions of thesubstrate with respect to the optical metrology or inspection head. 13.The apparatus of claim 12, wherein the purge gas distribution manifoldis within 10 percent of the surface area of the top surface of thesubstrate.
 14. The apparatus of claim 12, wherein the at least one portis a slot that has a length that is a radius of the substrate.
 15. Theapparatus of claim 12, wherein the purge gas comprises an inert gas. 16.The apparatus of claim 15, wherein the inert gas comprises at least oneof clean dry air, nitrogen, argon or a combination thereof.
 17. Theapparatus of claim 12, wherein the plurality of apertures in the purgegas distribution manifold is formed by a porous media.
 18. The apparatusof claim 12, wherein the plurality of apertures in the purge gasdistribution manifold is a pattern of holes.
 19. The apparatus of claim18, wherein the holes are coupled to distribution grooves.
 20. Theapparatus of claim 12, wherein the purge gas distribution manifold isheld linearly stationary with respect to the substrate when the at leastone of the chuck and the optical metrology or inspection head is movedto position the substrate at the plurality of measurement positions withrespect to the optical metrology or inspection head.
 21. The apparatusof claim 12, further comprising a fence surrounding the substrate on thechuck, wherein the fence is held linearly stationary with respect to thesubstrate when the at least one of the chuck and the optical metrologyor inspection head is moved to position the substrate at the pluralityof measurement positions with respect to the optical metrology orinspection head.
 22. The apparatus of claim 21, wherein the fencecomprises an upper surface that is 10 mm or less from a bottom surfaceof the purge gas distribution manifold.
 23. The apparatus of claim 12,further comprising a reference chip, wherein the purge gas distributionmanifold extends over the reference chip.
 24. An apparatus comprising:an optical metrology or inspection head that produces a light beam thatis incident on a substrate to be optically measured and is received bythe optical metrology or inspection head after interacting with thesubstrate; a chuck for holding the substrate, wherein at least one ofthe chuck and the optical metrology or inspection head is movable toposition the substrate at a plurality of measurement positions withrespect to the optical metrology or inspection head; a ceiling having atleast one port through which the light beam is transmitted, the ceilinghaving a bottom surface that is 25 mm or less from a top surface of thesubstrate; and a fence surrounding the substrate on the chuck, whereinthe fence is held linearly stationary with respect to the substrate whenthe at least one of the chuck and the optical metrology or inspectionhead is moved to position the substrate at the plurality of measurementpositions with respect to the optical metrology or inspection head, thefence having one or more apertures below the top surface of thesubstrate and through which purge gas is expelled over the top surfaceof the substrate to distribute the purge gas over an entirety of the topsurface of the substrate at all measurement positions of the substratewith respect to the optical metrology or inspection head.
 25. Theapparatus of claim 24, wherein the fence comprises an upper surface thatis 10 mm or less from the bottom surface of the ceiling.
 26. Theapparatus of claim 24, wherein the purge gas comprises an inert gas. 27.The apparatus of claim 26, wherein the inert gas comprises at least oneof clean dry air, nitrogen, argon or a combination thereof.
 28. Theapparatus of claim 24, wherein the one or more apertures are on a bottomsurface of the fence.
 29. The apparatus of claim 24, wherein the purgegas is exhausted through the at least one port in the ceiling.
 30. Theapparatus of claim 24, further comprising a reference chip, wherein thefence surrounds the substrate and the reference chip.